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Examining the Impact of a Beef Marbling Tolerance of 40, 

Ribeye Size and Marbling Texture

Lawrence Yates, Ph.D.

Standardization Branch

Quality Assessment Division

Livestock, Poultry and Seed Program

May 2015

Concerns have been expressed regarding the marbling tolerance of 100 for instrument marbling 

score overrides. The tolerance was deemed to be too wide to allow for the proper adjustment 

of inaccurate grades assigned by the camera thought to arise from carcasses having certain 

characteristics (e.g., large or small ribeye areas, coarse marbling).

In response to this concern, the Standardization Branch conducted a multiple-plant study to 

examine the impact of a marbling tolerance of 40. Further, data was collected to ascertain 

what effect ribeye size and marbling texture might have on marbling overrides. 

Methodology

Plants

The study was conducted at National Beef Packing Co. and Cargill Meat Solutions in Dodge City, 

KS and at Greater Omaha Packing Co. and Nebraska Beef, Ltd. in Omaha, NE. The study was 

conducted during two one-week periods in the April to May 2015 timeframe. Personnel 

consisted of two staff from the Standardization Branch (SB) as well as the Supervisory 

Agricultural Marketing Specialist (SAMS) for each selected plant. Three of the plants utilized 

instrument grading systems manufactured by e+v Technology GmbH & Co (e+v). Two of the 

plants used an e+v LED based system while the third plant used an e+v Xenon based system. 

The fourth plant used an instrument grading system manufactured by Research Management 

Systems, Inc. (RMS). 

Carcass Selection and Review

Carcasses were reviewed over a one to three day period in each plant. Carcasses were 

reviewed over several time segments in each plant where the first and last carcass ID for each 

segment was recorded. One SB staff assessed the carcass and instrument marbling at the four 

plants while the other SB staff recorded the carcass IDs, override marbling assessments and 

marbling texture scores. SAMS reviewed and measured the ribeye area (REA) for each of the 

override carcasses. Instrument data was subsequently collected from each plant for the 

carcasses reviewed. One plant was unable to provide carcass ID-linked hot carcass weights or 

REA for 779 carcasses. 

Statistical Analysis

All analyses used the procedures of SAS (SAS Inst. Inc.). Exploratory analyses were conducted 

using the MEANS, FREQ and UNIVARIATE procedures to characterize the review sample 
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distribution type as well as to characterize the reviewed carcasses. Analysis for differences was 

conducted using MIXED and GLM procedures. The main effects of plant (instrument), REA size 

and marbling texture were analyzed for differences between the instrument marbling and the 

SB assessed marbling. Mean separations were performed using Tukey-Kramer test, with a 

predetermined significance level of P<0.05. 

Results

Override Marbling Tolerance

The study reviewed 7,685 carcass to determine the impact of a marbling tolerance of 40 on 

overriding instrument marbling score. Further, the effect of ribeye size and marbling texture 

were also examined to ascertain any impact on marbling score overrides, a concern of USDA 

graders. Means for hot carcass weight, ribeye area, instrument marbling score, instrument and 

override quality grades are shown in Table 1. The factors have values and variation similar to 

those of the 2011 National Beef Quality Audit: an 825 ± 102 lb. hot carcass weight (± standard 

deviation); ribeye area of 13.8 ± 1.8 in2; marbling score of 440 ± 98; and a quality grade of 

Select93 ± 0.61 (1.93)1. The similarity of both value and variation for these carcass factors 

indicates that the carcasses reviewed were similar to the national carcass population. 

The review of 7,685 carcasses resulted in 5.3% marbling overrides (Table 2). 92.6% of the 

overrides were downgrades of the instrument marbling score to a lower value. The magnitudes 

of the override differences were similar for both the downgrades and upgrades for three of the 

four plants. There was no difference between Plant A, Plant B and Plant C but Plant D was 

significantly different (P<0.05) from the other three. Concerning upgrades and downgrades, 

the small number of upgrades precludes any firm conclusion in regards to the similarity 

between the magnitude of downgrades and upgrades. 

The percent of overrides by plant are presented in Table 3. Of the overrides, 89.6% had an 

override magnitude difference of 40 or more. Override percentages varied by plant as well as 

the percentage of overrides that equaled or exceeded a magnitude of 40. Marbling overrides 

that resulted in a change in quality grade varied by plant (Table 4). The inconsistency in 

qualifying overrides (≥ 40) was most likely related to two factors: one, chain speed and the 

positioning of the monitor relative to carcasses for each plant; and two, the e+v LED systems 

displayed the marbling score to three digits (391 for the LED based systems versus 390 for the 

Xenon based systems). 

Influence of Ribeye Area

The effect of ribeye size was examined to ascertain if there was any impact of large or small 

REA on marbling score overrides, a main concern expressed by USDA graders. To test the 

impact of small or large REA, the reviewed carcass sample was partitioned into 10th/90th and 

25th/75th percentiles. The 10th/90th percentiles were composed of three partitions: 1, the 

smallest 10% of the REA; 2, the middle 80% of the REA; and 3, the largest 10% of the REA. 

Likewise, the 25th/75th percentiles were composed of three partitions: 1, the smallest 25% of 

 

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Journal of Animal Science 2012 90: 13: 5152-5158
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the REA; 2, the middle 50% of the REA; and 3, the largest 25% of the REA. The two strategies 

for partitioning small/large REA were chosen to compare the results of the two since the 

10th/90th percentile partitions had so few override carcasses in the 10th and 90th percentiles. 

The larger number of carcasses in the 25th and 75th percentiles allowed for a more robust 

analysis. However, comparisons were always performed for both to ensure that any conclusion 

from small or large REA was consistent. In the end, the same conclusions were reached with 

both.

Table 5 presents the number of carcasses in each partition as well as the mean marbling score. 

With both methods, the mean marbling scores were different (P<0.05) from the other 

partitions within each method and the marbling scores decreased with increasing REA. 

Marbling override difference was impacted by REA size with the smallest REA being different 

(P<0.05) from the larger partitions (Table 6). However, there were fewer overrides associated 

with the smaller REA as compared to the medium and large partitions. There was also a plant 

difference (P<0.05) in that the Plant D differed from the other three. This was a consequence 

of the equipment manufacture since the RMS system was found to be different (P<0.05) from 

the e+v systems. The marbling override differences as a function of REA size between the two 

manufactures are similar in that the smaller REA partition was associated with larger override 

differences than the two larger partitions (P<0.05; Table 7). 

Figure 1 displays the marbling override difference as a function of REA. There does not appear 

to be a clear consistent trend associated with either the smaller or larger REA partitions other 

than the increased scatter as REA becomes smaller. The depicted scatter reflects the larger 

standard deviation (variability) of the 25th percentile partition (REA Size 1) of Tables 6 and 7. 

There were a higher number of overrides associated with the 75th percentile partition (REA Size 

3); 7.7% of the 75th percentile partition carcasses reviewed. The other two partitions had 4.0% 

and 4.2% for 25th percentile and the middle partitions, respectively. A review of the histograms 

of the three partitions (Figure 2) suggests that the 75th percentile partition had more carcasses 

surrounding the Slight00 and Small00 grade lines than the 25th percentile partition. 

The REA of carcasses deemed eligible for an override were assessed by SAMS. The difference 

between the instrument and SAMS assessed REA by plant is presented in Table 8. The average 

difference ranged from -0.03 to -0.65 in.2. There was much larger range in the standard 

deviations, 0.25 to 1.12. The performance requirements

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for operational accuracy, based on 

200 or more observations, specifies an R2of 0.85 or greater, 95% of the observations within 2.0 

in.2and the residual standard deviation should be within 1.00 in.2. Only one of the instrument 

plants had sufficient numbers to assess conformity, Plant A, and all parameters met the 

requirements. With respect to the other instrument plants, Plant B and Plant C met the 

residual standard deviation and 95% of the observations within 2.0 in.2requirements. The 

instrument at Plant D did not meet the requirements. With respect to instrument approval, an 

actual mean REA was based on the average from three experts or from acetate traced REA 

readings. As such, the performance of three out of the four instruments is consistent with the 

 

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USDA. Procedures for Approval and Use of Instrument Systems for Beef Carcass Ribeye Measurement, 2003
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prior approvals. However, the results for the Plant D instrument warrant a more thorough 

examination to ascertain if the performance is compliant with the performance standards.

Influence of Marbling Texture

The effect of marbling texture was examined to ascertain if there was any impact on marbling 

score overrides. The main concern expressed by USDA graders indicated that course marbling 

results in higher instrument marbling scores than what the marbling should be. This would 

suggest that as marbling became coarser, overrides would become more frequent and the 

marbling override difference would become larger. Table 9 summarizes the marbling override 

difference and the instrument marbling score by downgrades/upgrades, marbling texture and 

instrument manufacturer. For downgrades, marbling override difference was not influenced by 

marbling texture with the e+v instrument. In contrast, fine marbling texture was associated 

with a larger marbling override difference (P<0.05) than with medium or coarse marbling 

texture with the RMS instrument. More overrides were associated with the Small/Modest 

degree of marbling where marbling transitions from fine to medium texture. This was followed 

by the Slight/Small degree of marbling that encompasses the Slight00 and Small00 grade lines. 

The small number of upgrades precludes reaching any conclusion for either instrument 

manufacturer. 

Other Areas of Influence

An analysis of the 10s digit of both the SB staff and instrument marbling scores was conducted 

to ascertain areas of attention. Table 11 presents a cross-tabulation table that shows where 

the most frequent overrides occurred between the SB staff and the instrument. The 

predominant areas of overlap occurred at 60-00 (expert-instrument), 70-10 and 80-20. It was 

expected that 90-30 would also be one of the predominant occurrences but 90-30 area 

occurred 1% of the time. The areas of 80-30 and 80-40 occurred at a much higher frequency 

than 90-30. As the bottom of Table 10 shows, the 10s digit of the instrument was equally 

distributed across all digits while the expert’s distribution was located predominantly in the 50 

to 80 digits range. It was anticipated that the expert’s predominant override areas would have 

been in the 60 to 90 range, the cells marked by bold lines. The 90s digit will need to be an area 

of focus to ensure that all marbling scores are treated equitably. 

Economic Impact of the Proposed 40 Unit Override

The economic impact of the propose instrument override was assessed by determining carcass 

value. The grade distribution was used to establish the fiscal impact by using carcass premiums 

and discounts that are published weekly by the USDA Livestock, Poultry, and Grain Market 

News. Table 11 presents the grade distributions using four different approaches: the 

instrument quality grade before overrides are applied; the quality grade for all of the recorded 

overrides; the quality grade for only those overrides that were actually 40 and greater; and, the 

quality grade for those overrides that were 50 and greater. Of the recorded overrides, 10.4% 

were less than 40 so an override of 50 or greater was added based on the thought that an 

override of 50 would be easier to estimate than 40. Further, an override of 50 resulted in 

99.3% of the overrides being grade changes rather than 95.6% for an override of 40 (Table 4). 

A premium and discount per 1,000 carcasses was also estimated since a number of plants have 
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capacities in multiples of 1,000. There was variation between plants. Some of this was due to 

the frequency of overrides but some of this was also due to the carcasses that were graded 

during the review and their grade distribution.

Summary

A review of 7,865 carcasses resulted in 5.3% overrides using an override tolerance of 40. 

However, only 89.6% of those overrides were actually 40 or greater. The percentage of 

overrides did differ by plant and by instrument system. There was a slight effect due to REA 

size with smaller ribeyes having a higher override difference then the two larger REA sizes. 

With respect to marbling texture, there was no difference of texture with the e+v systems. The 

RMS system had larger override differences for the fine textured marbling. 
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Table 1. Means, standard deviations, and minimum and maximum values for USDA carcass

grade traits for the carcasses reviewed.

Factor Mean Std Dev Minimum Maximum N

Hot Carcass Weight 871 119 363 1,377 6,908

Ribeye Area 13.8 1.7 8.2 2 1 6,903

Marbling Score 502 117 180 1,050 7,685

Instrument Quality Grade 1.89 0.52 0 3 7,685

Override Quality Grade 1.84 0.55 0 3 7,685

Hot carcass weight: pounds.

Ribeye area: square inches.

Marbling Score: Traces 200, Slight 300, Small 400, Modest 500, Moderate 600, Slightly Abundant 700

Quality Grade: No Roll 0, Select 1, Choice 2, Prime 3.

Table 2. Override occurrence, means, standard deviations, and minimum and maximum values 

for the marbling override difference magnitude by plant. Note, upgrades are displayed using a 

negative value.

Plant # Carc Overrides Avg Std Min Max n Avg Std Min Max n

Plant A 2,229 148 -49 2 9 -82 -25 3 5 5 2 3 2 1 198 145

Plant B 2,070 8 5 -48 2 5 -80 -20 4 5 9 2 7 3 0 200 8 1

Plant C 1,899 4 2 -49 2 2 -113 -15 1 6 5 2 5 5 1 297 2 6

Plant D 1,491 130 -30 3 5 -10 -70 3 7 6 4 2 0 360 123

Total 5,460 257 2 3 230

Upgrades Downgrades

Table 3. Percentages of overrides and qualifying overrides by plant. 

Plant Overrides <40 ≥ 40

Plant A 6.6% 14.9% 85.1%

Plant B 4.1% 3.5% 96.5%

Plant C 2.2% 31.0% 69.0%

Plant D 8.7% 3.1% 96.9%

All 5.3% 10.4% 89.6%

Table 4. Percentage of marbling overrides that resulted in a quality grade change by plant.

Plant

Override

Grade Change

Plant A 98.0%

Plant B 97.6%

Plant C 81.0%

Plant D 96.2%

All 95.6%
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Table 5. Means and standard deviations for the instrument marbling score stratified by ribeye 

area size. 

REA Size n Mean Std Dev n Mean Std Dev

1 659 514a126 1,633 507a127

2 5,595 502b120 3,553 496b118

3 649 445c88 1,717 455c97

10th/90th Percentile 25th/75th Percentile

a, b, c Least squares means within a column lacking a common superscript letter differ (P < 0.05)

Marbling Score: Traces 200, Slight 300, Small 400, Modest 500, Moderate 600, Slightly Abundant 700

Ribeye size: 10th/90th percentile, 1 11.7 in2or smaller, 2 middle, 3 16.1 in2or larger; 25th/75th

percentile, 1 12.6 in2or smaller, 2 middle, 3 14.9 in2or larger 

Table 6. Means and standard deviations for the marbling override magnitude and instrument 

marbling scores stratified by override direction and ribeye area size. 

Override

Direction REA Size Mean Std Dev Mean Std Dev N

1 7 6 4 4 503 139 5 6

2 5 5 3 2 470 122 140

3 5 8 2 3 429 9 5 126

1 -48 2 2 453 156 9

2 -53 2 7 524 153 1 1

3 -33 1 7 443 133 6

Down

grade

Up

grade

Instrument Marbling

Marbling Override

Difference

Ribeye size: 1 25th percentile (12.6 in2or smaller), 2 middle 50%, 3 75

th percentile (14.9 in2

or larger) 

Table 7. Means and standard deviations for the marbling override magnitude stratified by 

override direction and ribeye area size by instrument manufacture. 

Override

Direction REA Size Mean Std Dev N Mean Std Dev N

1 6 7 3 7 3 6 9 2 5 2 2 0

2 5 1 3 2 109 6 9 3 1 3 1

3 5 7 2 1 107 6 7 3 3 1 9

1 -52 1 9 8 -10 - 1

2 -55 2 5 9 -40 4 2 2

3 -33 1 7 6 - - -

E+V

Down

grade

Up

grade

RMS

Ribeye size: 1 25th percentile (12.6 in2or smaller), 2 middle 50%, 3 75

th percentile (14.9 in2

or larger) 
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Table 8. Means and standard deviations of the difference between instrument and measured 

ribeye areas, and the percentage of the differences within the instrument performance 

requirement by plant.

Plant Mean Std Dev N

Plant A -0.09 0.73 96.2% 266

Plant B -0.65 0.90 96.0% 100

Plant C -0.03 0.25 100.0% 73

Plant D -0.33 1.12 88.2% 68

Within

2 inches2

Instrument REA

minus

Measured REA

Table 9. Means and standard deviations for the marbling override magnitude stratified by 

override direction and marbling texture by instrument manufacture.

Override

Direction Texture Mean Std Dev N Marbling Std Dev Mean Std Dev N Marbling Std Dev

1 5 7 2 5 7 9 391 4 1 9 8 5 8 4 0 447 4 0

2 5 6 3 2 160 430 6 1 6 6 2 8 8 2 572 8 2

3 5 0 1 1 1 3 555 171 6 4 2 7 5 726 5

1 -47 2 4 7 417 117 - - - - -

2 -50 2 4 1 3 466 130 -70 - 1 660 -

3 -46 8 3 548 236 -10 0 2 665 7

E+V RMS

Down

grade

Up

grade

Texture: 1 Fine marbling, 2 medium marbling, 3 coarse marbling

Table 10. Instrument and expert ten’s digit cross-tabulation.

0 10 20 30 40 50 60 70 80 90 Total

0 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 1%

10 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 1%

20 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 1%

30 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 1%

40 0% 0% 1% 0% 1% 0% 0% 0% 0% 0% 2%

50 2% 2% 1% 0% 1% 1% 1% 0% 0% 1% 8%

60 9% 6% 4% 3% 1% 2% 1% 1% 1% 1% 29%

70 4% 12% 8% 4% 3% 2% 1% 1% 0% 0% 34%

80 1% 3% 8% 5% 3% 1% 1% 1% 0% 1% 23%

90 0% 0% 0% 1% 0% 0% 0% 0% 0% 0% 1%

Total 18% 24% 21% 12% 10% 6% 4% 2% 1% 3% 100%

11% 10% 12% 9% 10% 9% 9% 10% 10% 10%

Instrument 10's Digit

Expert's 10's Digit

All Cx Reviewed (n=7,685)
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Table 11. Economic impact of the carcass premiums and discounts that would result from the 

change in quality grade distributions. Int QG, the instrument quality grade before overrides are 

applied; Ovr QG, the quality grade for all of the recorded overrides; Ovr 40 QG, the quality 

grade for only those overrides that were actually 40 and greater; and, Ovr 50 QG, the quality 

grade for those overrides that were 50 and greater.

Difference

Source No Roll Se Ch Pr CWT 800 lb Cx 1,000 Hd from Int QG

Int QG 0.47% 18.60% 72.64% 8.30% $ (1.21) $ (9.68) $ (9,684) $ -

Ovr QG 0.99% 21.54% 69.79% 7.69% $ (1.79) $ (14.34) $ (14,344) $ (4,660)

Ovr 40 QG 1.00% 21.21% 70.10% 7.69% $ (1.76) $ (14.05) $ (14,050) $ (4,367)

Ovr 50 QG 0.92% 20.16% 71.13% 7.79% $ (1.59) $ (12.73) $ (12,734) $ (3,050)

Premium/Discounts per:

LM_CT169 5-Area Weekly Wtd Average Direct Slaughter Cattle - Premiums and Discounts for the week of 

6/01/2015: Prime, $14.44; Choice, $0.00; Select, $(12.31); and Standard, $(25.46).
10

-200

-100

0

100

200

300

8 9 10 11 12 13 14 15 16 17 18 19 20 21 Magnitude of Override

Ribeye Area

Figure 1. Scatter graph of the relationship between marbling score override magnitude and 

ribeye area. The gold horizontal line represents a condition when the override magnitude 

would be zero. The two horizontal lines represent an override of 40 and -40. The two vertical 

dotted lines represent the ribeye area cutoffs for the 25th and 75th percentiles for ribeye area 

for the carcasses reviewed. 
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Figure 2. Histograms of carcass numbers as a function of marbling degree. Ribeye size: 25th

percentile (12.6 in2 or smaller), 75th percentile (14.9 in2 or larger). 

0

200

400

600

800

1,000

1,200

1,400

200 300 400 500 600 700 800 900

Number of Carcasses

Marbling Degree

25th Percentile

0

200

400

600

800

1,000

1,200

1,400

200 300 400 500 600 700 800 900

Number of Carcasses

Marbling Degree

Middle 50%

0

200

400

600

800

1,000

1,200

1,400

200 300 400 500 600 700 800 900

Number of Carcasses

Marbling Degree

75th Percentile